This application is based on application No 99-63797 filed in the Korean Industrial Property Office on Dec. 28, 1999, the content of which is incorporated hereinto by reference.
(a) Field of the Invention
The present invention relates to a transparent conductive thin film and its preparation method and more particularly to a transparent conductive thin film consisted of silicon oxides, antimony-tin oxides, and indium-tin oxides which has superior hardness, conductivity, and non-reflexibility, while at the same time providing a uniform surface in a timely and economically efficient manner, and a method for the preparation of the same.
(b) Description of the Related Art
Generally, antimony tin oxides (hereinafter referred to as ATO) and indium tin oxides (hereinafter referred to as ITO) thin films are being extensively used in monitors for blocking generated detrimental electromagnetic waves, in transparent electrodes of Liquid Crystal Display components, in anti-fogging heating layers for window glass, etc. Furthermore, ATO and ITO thin films can obtain non-reflexibility according to both the coating thickness and the alignment of silicon oxides and the above oxides. Hence, a monitor""s light reflection is decreased to produce vivid picture quality. This technique can also be applied to the ordinary glass, too.
Conventionally, a vacuum deposition method, a sputtering method, or the like etc. are widely known as methods for the preparation of above ATO and ITO thin films. However, compared with the present invention, there have been difficulties in terms of the economical and timely effectiveness in applying such coatings on large spacious windows or on car glass due to high equipment cost and coating area limits, although they can be applied to Liquid Crystal Displays, anti-fogging heating layers, etc.
A dip-coating method, spin-coating method, spray-coating method, and the like etc. are disclosed in Korean Patent Publication Nos. 94-25969 and 95-3458.
First, when a dip-coating method or spin-coating method among these methods is used, a sol of silicon oxides is prepared by mixing one to four parts water and ethanol, isopropanol, isobutanol, normal propanol, normal butanol, ethyl cellosolve, ethyl carbitol, etc. with one part tetra ethoxy silane, tetra methoxy silane, or some other silane based compound. Furthermore, this sol can be prepared by additionally adding non water soluble solvents such as benzene, toluene, etc. The prepared silicon oxide sol is coated as a coating solution to be cured at a temperature of from 50 to 120xc2x0 C. for a period ranging a few minutes to dozens of minutes.
On the other hand, a compound having as its main constituents tin and antimony, an inorganic acid of tin salts such as tin chloride hydrate, as a tin compound, an inorganic acid of antimony salts such as an antimony chloride hydrate, as an antimony compound, and an organic acid of tin salts or antimony salts can be used when preparing an ATO sol coating solution.
After a solution prepared using these compounds is coated by the above coating method, an ATO transparent thin film is manufactured by firing it at a high temperature of 300 to 1200xc2x0 C. for a period ranging from a few dozen minutes to a few hours.
Secondly, when the spray-coating method is used, a transparent conductive thin film is obtained by spraying the above ATO sol solution on it after the material on which a transparent thin film is to be formed is heated to over 400xc2x0 C.
Furthermore, an IT0 sol solution is coated using the above coating methods, wherein an inorganic acid of indium salts such as indium chloride hydrate or indium nitride hydrate, as an indium compound, and an inorganic acid of tin salts such as tin chloride hydrate, as a tin compound are used in order to prepare the IT0 sol. During the preparation of a transparent conductive thin film, indium-tin oxides, as compared to ATO, have the disadvantage of higher cost due to high priced indium, while they have an advantage in that surface resistance can be lowered to a level of 10xcx9c102 xcexa9/cm2.
However, the above methods have the following problems.
First, dozens of minutes are required to increase the temperature to a high temperature of between 300 to 1200xc2x0 C. during the coating firing. Additionally, superior conductivity and transparency are obtained through the firing and cooling that can take from a few dozen minutes to a few hours according to the temperature employed. Hence, there is a disadvantage in that process time losses are great since the firing time is so long and the cooling time also requires from a few dozen minutes to a few hours.
Secondly, there are various problems when the above is applied to a cathode-ray tube (CRT) or monitor after the preparing process has been finished and the device is completely assembled and holding a vacuum. These adverse effects are represented by the deterioration of internal fluorescent bodies and other components and the operation yield is decreased when the firing is done at a high temperature ranging from 300 to 1200xc2x0 C. for several hours.
The present invention is for solving the above problems and it is an object of the present invention to provide a method for the preparation of a transparent conductive thin film for stabilizing the process high temperature and shortening process time.
It is another object of the present invention to provide an ATO or ITO transparent conductive thin film having superior conductivity and outstanding transparency and hardness prepared by the above methods.
In order to accomplish the above objects, the present invention provides a method for the preparation of a transparent conductive thin film comprising the steps of:
a) preparing a sol solution of antimony-tin oxides (ATO) or indium-tin oxides (ITO);
b) forming a transparent coating layer on an outer surface of a cathode-ray tube using the sol solution of antimony-tin oxides (ATO) or indium-tin oxides (ITO); and
c) rapidly increasing a temperature of the transparent coating layer to a predetermined temperature, and rapidly cooling the transparent coating layer either immediately or after maintaining the predetermined temperature for up to 20 seconds.
The present invention can further comprise the step of coating a coating layer of silicon oxides in order for a transparent conductive thin film to obtain light non reflection effectiveness as a pre-treatment step prior to a step of forming a transparent coating layer according to the step b).
The present invention prepares an ATO or ITO sol solution in a method for forming a transparent layer using ATO or ITO when preparing a transparent conductive thin film. When using ATO, one antimony salt selected from the group consisting of tertiary antimony chloride, penta-antimony chloride, tertiary antimony fluoride, tertiary antimony iodide, and antimony acetate is dissolved by solvent so that one tin salt selected from the group consisting of quaternary tin chloride, secondary tin chloride, secondary tin acetate, quaternary tin acetate, secondary tin bromide, and quaternary tin bromide can have a content ratio of 1 to 15% in the preparation method of this sol solution. One or more of solvents selected from the group consisting of ethanol, normal butanol, isobutanol, normal propanol, isopropanol, methylisobutyl carbinol, cyclohexanol, 2-ethylhexanol, ethyl carbitol, and ethyl cellosolve are used as the above solvent.
In this process, the solution is refluxed at a temperature of 50 to 90xc2x0 C. for hours, 2 to 20 equivalent weights of tertiary distilled water per tin equivalent weight are mixed in, and it is again refluxed at the above temperature for hours. Hydrochloric acid, acetic acid, iodic acid, bromic acid, hydrofluoric acid, and the like are removed by drying this prepared solution at a temperature of 150xc2x0 C. until it becomes powder. This is because coating capability is deteriorated due to the acidic effects of hydrochloric acid and other acids. After executing the above drying procedure, the sol solution containing 1 to 15% of solid contents suitable for coating is prepared using one or more of the above solvents.
An ITO sol solution preparation is also the same as in the above ATO preparation method, and one salt selected from the group consisting of primary indium chloride, tertiary indium chloride, tertiary indium fluoride, tertiary indium hydroxide, primary indium iodide, and tertiary indium acetate is used as an indium salt.
Accordingly a transparent coating layer is formed with this prepared sol solution on the outer surface of glass, including a CRT tube, using a dip-coating method, spin-coating method, spray-coating method, or the like, and is heated to a predetermined temperature, and then fired by the Rapid Thermal Annealing (RTA) method.
A preparation method of a transparent conductive thin film of the present invention can further comprise a primary drying step at a temperature of 60 to 250xc2x0 C. for one to thirty minutes before the firing step of the above c).
Furthermore, the preparation method of the present invention further comprise, a step of Rapid Thermal Annealing, wherein the Rapid Thermal Annealing method is carried out under nitrogen or argon gas environment.
Furthermore, the step b) of the present invention provides a preparation method of a transparent conductive thin film which is coated by a dip-coating method, a spin-coating method, or a and spray-coating method.
Furthermore, the present invention provides a preparation method of a transparent conductive thin film, wherein the firing temperature is from 300 to 1200xc2x0 C. in order to obtain the conductivity in the step c), the rate of increasing the temperature to the above temperature is from 100 to 500xc2x0 C./sec, and the temperature is rapidly cooled either immediately after the step c) achieves a temperature of between 300 and 1200xc2x0 C. or after maintaining for up to 20 seconds a temperature of between 300 and 1200xc2x0 C. achieved by the step c).
Furthermore, the present invention provides a transparent conductive thin film that is prepared according to the above preparation method.
The present invention further provides a transparent electrode of a Liquid Crystal Display component that is prepared according to the above preparation method.
The present invention still further provides an anti-fogging heating layer for window glass that is prepared according to the above preparation method.